Peter D. Keisler

Keisler, Peter D.


Washington, D.C. +1 202 736 8027

1501 K Street, N.W.
Washington, D.C. 20005
+1 202 736 8027

Admissions & Certifications

Peter D. Keisler


PETER D. KEISLER, a former Acting Attorney General of the United States and a co-leader of Sidley’s Supreme Court and Appellate practice, has successfully represented some of the country’s largest companies in the telecommunications, transportation, energy and healthcare industries, as well as a host of national trade associations, providing extensive insight and experience gained from his more than 25 years of private and public sector experience. Including him in its top-tier of the nation’s appellate lawyers, Chambers USA 2014 notes that clients told the directory that Peter “is one of the top appellate litigators in the country at this time. He has incredible mastery of appellate argument, and how to submit the most compelling case to federal judges.”

Peter has argued a wide range of federal constitutional, statutory, and administrative law cases. His practice representing clients before the U.S. Supreme Court, federal courts of appeals and federal district courts has included the leading role in the nation’s most important energy lawsuits of the past several years, including UARG v. EPA, AEP v. Connecticut, EME Homer City Generation LP v. EPA, and United States v. Cinergy Corp.

Peter’s recent arguments before the U.S. Supreme Court include:

  • Utility Air Regulatory Group v. Environmental Protection Agency (UARG v. EPA). Peter successfully argued that the EPA has no authority to impose permitting obligations on a source based solely on its emissions of greenhouse gases.
  • American Electric Power Co. v. Connecticut. Peter successfully represented four utility companies in this case, in which the Court unanimously reversed the court of appeals and held that states and private parties could not seek judicially-imposed reductions in greenhouse gas emissions against electric utilities under a federal common-law nuisance theory. The leading Supreme Court blog called this litigation “the biggest-ever case on the issue of global warming” and AmLaw Media named Peter its “Appellate Lawyer of the Week” for the argument, calling the case “one of the biggest environmental cases of the decade, if not the century.” 
  • National Cable & Telecommunications Association v. Gulf Power. Peter successfully argued on behalf of the cable television industry in this case, in which the Court held that cable operators offering high-speed Internet service are entitled to access to electric utility poles at regulated rates.
  • Roberts v. Sea-Land Services, Inc. Peter successfully argued on behalf of the respondent in this case involving the construction and application of federal worker compensation laws.

Peter is widely recognized as a leader in his field. Peter was named Best Lawyers’ “2016 Washington DC Appellate Practice ‘Lawyer of the Year.’” In 2012, the National Law Journal/Legal Times named Peter to its list of “Champions & Visionaries,” a select group of “attorneys whose business foresight or legal acumen has expanded their firms, advanced the law or improved government.” The NLJ noted that Peter “has been front and center in almost every major energy lawsuit in the past two years.” Since 2011, Peter has been recognized in Benchmark Litigation for his appellate practice and has also been included in the “Best Lawyers in America” directory for his appellate, commercial litigation and media law work. Law360 named Peter one of its “MVPs” for Appellate Law (2014) and Energy Law (2011). Chambers USA 2013 noted that Peter “is singled out as ‘one of the most extraordinary advocates’ for his outstanding work on behalf of clients from a wide range of industries.” Washingtonian magazine has included Peter on its 2013 list of Washington’s Best Lawyers as one of the region’s “best legal minds” for his Supreme Court practice. In 2014, Peter was featured in a Greenwire article “If the Clean Air Act’s on the docket, Keisler’s on the case.”

Peter started his career at Sidley as an associate in 1989 after completing a clerkship for Justice Anthony Kennedy. In 2002 he joined the Department of Justice (DOJ) as the Principal Deputy Associate Attorney General. Peter spent most of his more than five-year tenure at DOJ as the Assistant Attorney General for the Civil Division, and ultimately served as Acting Attorney General of the United States. He returned to Sidley in 2008.


Recent cases handled by Peter include:

  • Utility Air Regulatory Group v. EPA, No. 12-1146 (L). 
  • United States ex rel. Fair Laboratory Practices Associates v. Quest Diagnostics Incorporated, 734 F.3d 154 (2d Cir. 2013). 
  • National Association of Manufacturers v. SEC, 800 F.3d 518 (2015). 
  • American Electric Power Co. v. Connecticut, 131 S. Ct. 2527 (2011). 
  • National Cable & Telecommunications Association v. Gulf Power, 534 U.S. 327 (2002). 
  • Roberts v. Sea-Land Services, Inc., 132 S. Ct. 1350 (2012). 
  • United States v. Cinergy Corp., 623 F.3d 455 (7th Cir. 2010). 
  • Monarch Consulting v. National Union Fire Insurance Company, 26 N.Y.3d 659 (2016).
  • Medicines Company v. Kappos., 462 F. App’x 974 (Fed. Cir. 2012), 731 F. Supp. 2d 470 (2010). 

In these and other matters, Peter draws upon a wealth of experience gained from his notable government service. As Acting Attorney General of the United States—the chief law enforcement officer of the country—Peter directed the work of the Department of Justice, including its investigative agencies and litigating divisions. In his role as Assistant Attorney General for the Civil Division, Peter oversaw the work of the Justice Department’s largest litigating division, consisting of approximately 700 attorneys who represent the interests of the United States in federal and state courts throughout the country on a wide range of cases, including cases relating to administrative law, constitutional law, government contracts, False Claims Act and other civil fraud enforcement, bankruptcy, intellectual property, tort law, immigration law, foreign law, the constitutionality of federal statutes, the lawfulness of government programs and their implementation, national security matters, and civil and criminal enforcement of the Food, Drug and Cosmetic Act and other consumer protection laws. As head of the Civil Division, Peter personally argued a number of significant cases on behalf of the government involving issues of constitutional, statutory, regulatory and common law.

Peter also served as Associate Counsel to the President in the Office of White House Counsel under President Ronald Reagan.

Memberships & Activities

In addition to his role as co-leader of Sidley’s nationally recognized Appellate practice, Peter is a member of the firm’s Executive Committee. 

Peter was appointed by the Chief Justice to serve as a member of the Judicial Conference Committee on Rules of Practice and Procedure.

News & Achievements